1. Field of the Invention
The present invention relates to a process for the formation of single crystals from the gas phase, in which the single crystal which is located in the gas phase, and which as in the process of growth adhering with only one surface, is subjected to a static temperature gradient between the exposed crystal surface and the surroundings of the crystal. The invention furthermore relates to an arrangement for the implementation of the process.
2. Discussion of the Prior Art
Processes for the formation of monocrystals or single crystals from the gas phase are currently known in the art. In general, processes of that type have the common goal to grow crystals which are as devoid as possible from structural imperfections. Hereby, of particular significance is the control of the heat transport from the crystal surface to the wall of the growth vessel and the surrounding crystal surfaces, wherein in the known processes of the above-mentioned type the temperature gradient, besides the other necessary requirements, such as the adjustment of the metastable range of the supersaturation, is so adjusted that the temperature on the crystal surface is lower than that of the surroundings about the crystal.
The previously known processes are, however, unsatisfying to the extent in that, as a rule, they do not facilitate the growth of crystals of larger dimensions which are devoid of structural imperfections.
Moreover, other known processes in which the heat transport is controlled in a specialized manner, do not lead to the results which are sought after by the technology. Thus, for example, pursuant to the known process as disclosed by Scholz and Kluckow (Temperature-Gradient Reversal Methods for Crystal Growth, Crystal Growth Ed. H. S. Peiser, Pergamon, Oxford (1967), 475-482), the heat discharge is periodically varied through the cooling contact on the growth vessel. Hereby, at some locations on the growing vessel, the temperature gradient is directed from the wall towards the crystal and at other locations from the crystal towards the wall. In accordance with another known process (J. Omaly, M. Robert, R. Cadoret, Mat. Res. Bull., Vol. 16, (1981), 1261-1270) there is undertaken the formation of HgI.sub.2 (.alpha.) single crystals in a three isothermal zone furnace. Hereby, the crystal grows between Zone 1 and Zone 3, whereby the temperature is somewhat higher at the bottom of the vessel and the temperature is lower at the other end of the vessel. In both of the two known processes, however, there are obtained temperature differences within the crystal itself, in the first-mentioned known process additionally varying during the course of time, so as to produce stresses in the crystal which will lead to imperfections in the structural composition of the crystal.
In a further known processes (G. E. Gottlieb, Journal of the Electrochemical Society, Vol. 112, No. 9, (1965), 903-906) through the stepwise increase of the cooling contact which is applied to the adhering surface of the crystal, an attempt is made to discharge the heat through the increasing crystal in order to achieve that the crystal will be bound only by crystallographic planes. Also in this known process stresses are generated in the crystal which lead to structural imperfections.